Re: [PATCH bpf-next v2 0/2] bpf, bpftool: Support dumping kfunc prototypes from BTF

[Andrii Nakryiko]

On Sun, Feb 4, 2024 at 1:06 PM Daniel Xu <dxu@xxxxxxxxx> wrote:
>
> This patchset enables dumping kfunc prototypes from bpftool. This is
> useful b/c with this patchset, end users will no longer have to manually
> define kfunc prototypes. For the kernel tree, this also means we can
> drop kfunc prototypes from:
>
>         tools/testing/selftests/bpf/bpf_kfuncs.h
>         tools/testing/selftests/bpf/bpf_experimental.h
>
> Example usage:
>
>         $ make PAHOLE=/home/dxu/dev/pahole/build/pahole -j30 vmlinux
>
>         $ ./tools/bpf/bpftool/bpftool btf dump file ./vmlinux format c | rg "__ksym;" | head -3
>         extern void cgroup_rstat_updated(struct cgroup *cgrp, int cpu) __weak __ksym;
>         extern void cgroup_rstat_flush(struct cgroup *cgrp) __weak __ksym;
>         extern struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags) __weak __ksym;
>
> Note that this patchset is only effective after the enabling pahole [0]
> change is merged and the resulting feature enabled with
> --btf_features=decl_tag_kfuncs.
>
> [0]: https://lore.kernel.org/bpf/cover.1707071969.git.dxu@xxxxxxxxx/
>
> === Changelog ===
>
> From v1:
> * Add __weak annotation
> * Use btf_dump for kfunc prototypes
> * Update kernel bpf_rdonly_cast() signature
>
> Daniel Xu (2):
>   bpf: Have bpf_rdonly_cast() take a const pointer
>   bpftool: Support dumping kfunc prototypes from BTF

I've applied patch #1 as it's a good change regardless. Please send v2
for patch #2.

>
>  kernel/bpf/helpers.c    |  4 ++--
>  tools/bpf/bpftool/btf.c | 45 +++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 47 insertions(+), 2 deletions(-)
>
> --
> 2.42.1
>